Procedure for surface treatment of wood

ABSTRACT

A wood treatment involving pretreatment of the wood surface with an agent facilitating penetration of impregnant into said surface, a pretreatment agent being chosen in the form of a condensable or polymerisable, hyrophilic substance in liquid form, which is free from solvent and causes the wood to swell or dissolves its constituents, with which substance the wood surface is pretreated and impregnated, to a depth of a few millimetres, after which the substance is caused to harden either by subsequent treatment with harderners and heat treatment or by corresponding subsequent treatment with an agent which can be caused to react with the pretreatment agent under formation of a polymer. The pretreatment takes place with a solution of formaldehyde and/or low molecular paraformaldehyde in phenol or substituted phenol, and the so pretreated wood is treated with acid or alkaline vapours for starting of hardening, and further a heat treatment is added which may be combined with a mechanical treatment of the wood surface.

I United States Patent 1 1 1111 3,912,836

Johansson Oct. 14, 1975 [54] PROCEDURE FOR SURFACE TREATNIENT 2,674,5434/1954 Iablokoff 117/59 0F WOOD 2,740,728 4/1956 Sonnabend etal. 117 592,947,648 8/1960 Sonnabend et al. ll7/59 Inventor: Karl lngvar GeorgJohansson, 3,219,473 11/1965 Dimond 117/148 Spanga, Sweden 3,476,58511/1969 Fraser 1 17/57 3, 4 ,679 1219 M [73] Assgneei Gustav 3,232,1991i197 .leiil et al. 11 13 Valberg, Sweden [22] Filed: Apr. 25, 1973Primary Examiner-Michael Sofocleous [21] Appl. No.: 354,446

[57] ABSTRACT Related Apphcatlon Daw A wood treatment involvingpretreatment of the wood [63] continuationin'part of 351,161 Apfilsurface with an agent facilitating penetration of im- 1973 abandonedpregnant into said surface, a pretreatment agent being I chosen in theform of a condensable or polymerisable, [3O] Forelg Apphcauon PnontyData hyrophilic substance in liquid form, which is free from Apr. 27,Sweden olvent and auses the wood to well or dissolves its constituents,with which substance the wood surface is U-S- pretreated and impregnatedto a of a few Int. CL2 t H metres after the Substance is aused to hardenField of Search 117/148, 62; 427/317, 1 either by subsequent treatmentwith harderners and 427/341, 393, 397, 440 heat treatment or bycorresponding subsequent treatment with an agent which can be caused toreact with References Cited the pretreatment agent under formation of apolymer.

UNITED STATES PATENTS The pretreatment takes place with a solution ofform- 2,114,784 4/1938 Maisch 117/57 aldehyde and/or low molecularParaformaldehyde in 2 9 2 19 3 Booty er 117 59 phenol or substitutedphenol, and the so pretreated 2,174,132 9/1939 Maisch 1 17/ 148 wood istreated with acid or alkaline vapours for start- 2 ,33(),826 10/1943Hunn 117/148 ing of hardening, and further a heat treatment is 3 1 1944stammm- 1 17/148 added which may be combined with a mechanical 2,352,7407/1944 Shannon 117/59 treatment f the wood surface. 2,363,658 ll/l944Decker ll7/l48 2,572,070 lO/l95l Stamm et al 1 17/57 5 Claims, N0Drawings PROCEDURE FOR SURFACE TREATMENT O WOOD The present applicationis a continuatiori-in-part of my earlier application Ser. Number 351,161filed Apr. 16, 1973 now abandoned. w

The French Patent No. 2,1 13,481 relates to a procedure for surfacetreatment of wood, the surface layer of the .wood being pretreated withan agent which facilitates penetration of impregnant into the woodsurface f Characteristic of said patent is that as pretreatment agent isused a condensable or polymerizable, hydrophilic substance in liquidform, free from solventgcausing the wood to swell or dissolving woodconstituents, with which substance the wood surface is pretreated andimpregnated, preferentially to a depth of at most a few millimetres buteven up to one-fifth of the thickness of the wood, after which thesubstance is caused to harden either by subsequent treatment withhardeners and heat treatment or by corresponding subsequent treatmentwith an agent which can be caused to react with the pretreatment agentunder formation of a polymer.

The object of the present invention is to further develop said surfacetreatment procedure and to indicate treatment agents usable forindustrial application.

The invention is characterized in that the pretreatment is done with asolution of formaldehyde and/or low molecular paraformaldehyde in phenoland/or substituted phenol, and in that the so pretreated wood is treatedwith acid or alkaline vapours for starting .of the hardening reaction,and that an, in itself, known heat treatment takes place, which may becombined with a likewise known mechanical treatment of the wood surface.

According to one embodiment the pretreatment is done at elevatedtemperature, after which the hardening is done by subsequent treatmentwith ammonia in gaseous form and heating.

Alternatively the pretreatment can be done at room temperature and tothe pretreatment agent is added an ammonium salt of a strong acid, e.g.ammonium chloride or some other salt, e.g. AlCl which at roomtemperature does not appreciably affect the pretreatment agent but inthe subsequent treatment is decomposed by heat and gives off gases, sothat hardening of the pretreatment agent occurs.

The pretreatment can be done at atmospheric pressure or a slightoverpressure, the pretreatment agent being caused to penetratepreferentially into cell walls and cavities in the surface layer of thewood. Alternatively the pretreatment can be done at elevated pressure,the pretreatment agent being caused to penetrate more deeply, afterwhich the hardening is done at elevated temperature.

The invention will] now be explained in greater detail with reference tosome embodiments.

EXAMPLE 1 Boards of pinewood are impregnated with a solution offormaldehyde in phenol in the proportion (weight) 1:1.8 obtained eitherthrough coalescence of paraformaldehyde and phenol or through absorptionof gaseous formaldehyde in molten phenol at 60-l00C and at anoverpressure of 1-5 kp/cm during 30-60 min. The impregnation solution istapped off and the impregnation container is filled with ammonia gas toan overpressure of 0.5-2 kp/cm during 30-60 min, after which the woodmaterial is heated to -100C for l-4 hours. If a glossy surface of thematerial is desired, a hot pressing operation can finally be done, e.g.at an overpressure of 2-10 kp/cm and C for l-lO min. The boards sotreated, which, dependent on the thickness of the wood, contain 10-20plastic concentrated at the surface layer of the wood, have a verysatisfactory hardness and abrasion resistance and can suitably be usedas floor material.

EXAMPLE 2 Boards of spruce are impregnated with a solution of 1 part byweight formaldehyde in 1.8 parts by weight of a mixture of phenol and ahalogenized phenol, e.g. p-chlorophenol, at 60-100C. For this purposethe boards are placed in a pressure cylinder of conventional type andsubjected to a'slight overpressure of l-4 kp/cm The pre-treatmentsolution is then pumped into the cylinder and the pressure is raisedto10-15 kp/cm so that a quicker and deeper penetration of the woodmaterial is obtained. After 0.5-3 hours the remaining pretreatment agentis tapped out of the cylinder and, owing to the pressure applied inadvance, the solution which has not penetrated into the cell walls isnow pressed out of the wood, so obtaining an impregnation primarily ofthe cell walls. Thereafter the impregnation container is filled withammonia gas to an overpressure of 0.5-2 kp/cm for 30-60 min. and thematerial is then heated to 80-100C for 1-4 hours. This produces a woodmaterial containing 10-30 plastic with very good strength properties, anexcellent dimensional stability and good fire resistance, which issuited for use under severe conditions out-of-doors.

EXAMPLE 3 Pieces of plywood are immersed in a solution of formaldehydein phenol in the proportion 1:1.8, in which is dissolved 0.5-5 ammoniumchloride. The pieces of wood are left to absorb the solution during15-60 min. and are then taken up and heated in a heating furnace at80-l00C for l-2 hours. The resulting product has a good abrasionresistance and ability to resist both water and alkali.

EXAMPLE 4 The surface chips for chipboards are sprayed with a solutionof formaldehyde in phenol in the proportion 1:1.8 in which 0.5-5ammonium formate has been dissolved. The weight of added solution is10-50 of the weight of the surface chips. The spreading and compressionof the surface chips are done in the conventional way at, for example C,20 kp/cm and 5 min, and the resulting chipboard has considerablyimproved surface density properties.

EXAMPLE 5 Veneer is treated on both sides with a solution offormaldehyde in phenol as in the preceding example, is hardened and usedas surface layer, possibly also intermediate layer, for the manufactureof plywood, which thereby acquires good abrasion resistance, excellentadhesion between the layers and good water repelling properties.

EXAMPLE 6 Telegraph poles, fencing poles, railway sleepers or similarheavy timber, are impregnated with a solution of formaldehyde in phenolin the proportion 1:1.8 for 1-2 hours at 60100C and at an overpressureof 2-10 kp/cm Thereafter the impregnation solution is tapped off and theimpregnation tank is filled with NH gas to an overpressure of 1-5 kp/cmat a temperature of 80l00C for 1-2 hours. The wood material so treatedcontains 5-15% plastic to a depth of 5-15 mm, which gives it anexcellent surface hardness, a good rotproofness and an improved flexuralstrength. The thickness of the treated surface layer permits, forexample, the use of climbers on telegraph poles treated in this waywithout breaking through the resulting surface layer.

EXAMPLE 7 Dried plywood veneer is immersed in a solution of formaldehydein phenol in the proportion 1:1.8 for 1-10 min at 0-2 kp/cmoverpressure. The sheets of veneer are prehardened in a heating furnaceat 50l00C in an ammonia gas atmosphere for -6O min and are thereafterused in the conventional way as face veneer in plywood manufacture. Theresulting plywood product has an excellent surface hardness and abrasionresistance and good resistance to moisture and alkali.

What is claimed is:

l. A process for the surface-treatment of wood, which comprisespretreating a wood substrate at a temperature between about 60lOOC. forabout 1 to 2 hours with a hydrophilic liquid material, that issubstantially free of any solvent and that causes the wood to swell ordissolves constituents of the wood, until the desired depth ofpenetration has been attained; said hydrophilic liquid materialconsisting of a condensable solution of formaldehyde in phenol in theweight ratio of about 1:1.8; and thereafter at a temperature betweenabout 50and about 150C. treating the resulting pretreated wood with acondensing agent for a time sufficient to obtain a hardened condensateof said hydrophilic material in the form of an abrasion resistantsurface.

2. A process according to claim 1, in which the treating agent isgaseous ammonia.

3. A process according to claim 1, in which the formaldehyde is presentas paraformaldehyde.

4. A process for the surface-treatment of wood, which comprisespretreating a wood substrate at room temperature with a hydrophilicliquid material, that is substantially free of any solvent and thatcauses the wood to swell or dissolves constituents of the wood, untilthe desired depth of penetration has been attained; said hydrophilicliquid material consisting of a condensable solution of formaldehyde anda heatdecomposable ammonium salt in phenol in which the weight ratio offormaldehyde to phenol is about 1:1.8; and thereafter heating thepretreated wood at a temperature of about to about C for a timesufficient to decompose the ammonium salt to ammonia and to obtain ahardened condensate of said hydrophilic material in the form of anabrasion resistant surface.

5. A process according to claim 4, in which the heatdecomposableammonium salt comprises ammonium chloride.

1. A PROCESS FOR THE SURFACE-TREATMENT OF WOOD, WHICH COMPRISESPRETRETING A WOOD SUBSTRATE AT A TEMPERATURE BETWEEN ABOUT 60*-100*C.FOR ABOUT 1 TO 2 HOURS WITH A HYDROPHILIC LIQUID MATERIAL, THAT ISSUBSTANTIALLY FREE OF ANY SOLVENT AND THAT CAUSES THE WOOD TO SWELL ORDISSOLVES CONSTITUENTS OF THE WOOD, UNTIL THE DESIRED DEPTH OFPENETRATION HAS BEEN ATTAINED, SAID HYDROPHILIC LIQUID MATERIALCONSISTING OF A CONDENSABLE SOLUTION OF FRMALDEHYDE IN PHENOL IN THEWEIGHT RATIO OF ABOUT 1:1.8, AND THEREAFTER AT A TEMPERATURE BETWEENABOUT 50* AND ABOUT 150*C. TREATING THE RESULTING PRETREATED WOOD WITH ACONDENSING AGENT FOR A TIME SUFFICIENT TO OBTAIN A HARDENED CONDENSATEOF SAID HYDROPHILIC MATERIAL IN THE FORM OF AN ABRASION RESISTANTSURFACE.
 2. A process according to claim 1, in which the treating agentis gaseous ammonia.
 3. A process according to claim 1, in which theformaldehyde is present as paraformaldehyde.
 4. A process for thesurface-treatment of wood, which comprises pretreating a wood substrateat room temperature with a hydrophilic liquid material, that issubstantially free of any solvent and that causes the wood to swell ordissolves constituents of the wood, until the desired depth ofpenetration has been attained; said hydrophilic liquid materialconsisting of a condensable solution of formaldehyde and aheat-decomposable ammonium salt in phenol in which the weight ratio offormaldehyde to phenol is about 1:1.8; and thereafter heating thepretreated wood at a temperature of about 80*to about 150*C for a timesufficient to decompose the ammonium salt to ammonia and to obtain ahardened condensate of said hydrophilic material in the form of anabrasion resistant surface.
 5. A process according to claim 4, in whichthe heat-decomposable ammonium salt comprises ammonium chloride.